1. Field of the Invention
The present invention relates to a communication system, a communication method and a storage medium for the system, which are applicable to a facsimile machine having a memory function, a complex copying machine having a communication function and an information terminal having a communication function for prevention of a communication failure which may occur due to a shortage of free memory space in a receiver terminal.
2. Description of the Related Art
In recent years, facsimile machines having a memory function have become widely available. Such a facsimile machine is adapted to transmit data after storing the data in a memory when functioning as a transmitter terminal, so that the data can be re-transmitted even if a line is busy. Further, the facsimile machine is adapted to print out received data after temporarily storing the data when functioning as a receiver terminal.
When a great amount of received data is accumulated in the memory of the receiver terminal, however, the data overflows the memory during the data reception, so that data thereafter received cannot be stored in the memory. This causes a communication failure due to a shortage of the capacity of the memory.
One conventional approach to this problem is a facsimile communication method disclosed, for example, in Japanese Unexamined Patent Publication No. 2-216972 (1990). In this method, a receiver terminal transmits a communication protocol signal containing information of an available memory space (residual memory capacity) to a transmitter terminal, and the transmitter terminal transmits data to the receiver terminal in accordance with the residual memory capacity of the receiver terminal.
Japanese Unexamined Patent Publication No. 6-113086 (1994) proposes a facsimile machine, which is adapted to reduce the pixel density (resolution) of received image data to store a reduced amount of the image data when a residual memory capacity of an image memory thereof is reduced to lower than a predetermined level, and request a transmitter terminal to re-transmit the original image data thereto when the residual memory capacity of the image memory is restored to not lower than the predetermined level.
Japanese Unexamined Patent Publication No. 10-164331 (1998) proposes a facsimile machine, which is adapted to transmit a memory-over signal to a transmitter terminal and disconnect a line, when an image memory thereof becomes full, to cause the transmitter terminal to stop transmitting image data and store pages of image data and, when a free space in the image memory is increased, call the transmitter terminal to cause the transmitter terminal to transmit thereto the stored image data pages.
The facsimile machines disclosed in Japanese Unexamined Patent Publication Nos. 2-216972, 6-113086 and 10-164331 cause the transmitter terminal to transmit the data in accordance with the residual memory capacity of the memory upon reception of information that the residual memory capacity of the memory is reduced, and re-transmit the data upon reception of information that the free space in the memory is restored for prevention of a communication failure due to the shortage of the free memory space.
Where the data is transmitted in accordance with the residual memory capacity of the memory, the transmitter terminal should transmit a portion of the data untransmitted at the previous data transmission or all the data again to the receiver facsimile machine. Thus, the transmitter terminal has to perform unnecessary data transmission or wait for notification of the recovery from the shortage of the free memory space. Therefore, time until the transmission is permitted cannot efficiently be utilized.
In view of the foregoing, the present invention is directed to a communication system and a communication method, which can suppress unnecessary inquiry between a transmitter terminal and a receiver terminal and time-wasting data transmission to the receiver terminal, when a storage section of the receiver terminal is short of free space, by preliminarily providing a waiting period required for recovery from the shortage of the free space in the storage section of the receiver terminal and causing the transmitter terminal to transmit data after the lapse of the waiting period. The invention is further directed to a storage medium for the communication system.